Evaluation of an Aerosol Activation Parameterization Christos Fountoukis

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Evaluation of an Aerosol Activation Parameterization Christos Fountoukis April 19, 2004 EAS: Atmospheric Chemistry

Evaluation of an Aerosol Activation Parameterization Christos Fountoukis April 19, 2004 EAS: Atmospheric Chemistry Term Paper

Summary • The new aerosol activation parameterization • The adiabatic cloud parcel model •

Summary • The new aerosol activation parameterization • The adiabatic cloud parcel model • Evaluation of the parameterization for a wide range of: – Chemical variability – CCN (cloud condensation nuclei) concentrations – Updraft velocities, temperatures, pressures • Conclusions

Aerosol activation parameterization • Developed in two steps: – Representation of the aerosol number

Aerosol activation parameterization • Developed in two steps: – Representation of the aerosol number and the chemical composition distribution with respect to size and calculation of the CCN spectrum – Determination of the maximum supersaturation by a numerical solution of an algebraic equation and calculation of droplet number concentration from the supersaturation spectrum

Sectional representation of size distribution

Sectional representation of size distribution

CCN spectrum

CCN spectrum

Droplet number concentration estimation Once the maximum parcel supersaturation, smax, is known, the number

Droplet number concentration estimation Once the maximum parcel supersaturation, smax, is known, the number of CCN that will activate into drops, Nd, is given by

Adiabatic cloud parcel model • Based upon the parcel model described by Seinfeld and

Adiabatic cloud parcel model • Based upon the parcel model described by Seinfeld and Pandis, (1998). • Resolves numerically a set of differential equations that describe the rate of growth of a drop of diameter Dp • Determines the droplet diameter at the time of maximum supersaturation

Simulations for different conditions • • • Ntotal (cm-3) σ Dp, g (μm) W

Simulations for different conditions • • • Ntotal (cm-3) σ Dp, g (μm) W (m/s) Cloud height (m) Chemical composition 100, 500, 1000, 5000, 10000 1. 1, 1. 2, 1. 5, 2. 0, 2. 5 0. 025, 0. 05, 0. 75, 0. 25 0. 1, 0. 3, 1. 0, 3. 0 500 (NH 4)2 SO 4: 100%, (NH 4)2 SO 4: 50%-insoluble: 50%, Na. Cl: 100%, Na. Cl: 25% - insoluble: 75 • • Accommodation coefficient Pressure (mbar) Relative humidity Temperature (K) 0. 005, 0. 01, 0. 1, 1 800, 1000 90%, 98% 273, 303

Results

Results

Results (2)

Results (2)

Results (3)

Results (3)

Conclusions • For the wide variety of aerosol characteristics, very good agreement between the

Conclusions • For the wide variety of aerosol characteristics, very good agreement between the two models • Systematic biases for: – Insoluble species – Species with low accommodation coefficient • The open structure of the parameterization allows for further extension (include condensable gases, organics, etc. )